A money market fund invests in safer assets which are liquid and only purchasing high rated debt for a short period of time. Those who invest in money market funds are looking for a better alternative to a checking account as far as yields are concerned and it is very common to see brokerage clients utilize the money markets as well, when the funds are not invested in the markets. Just like a checking account, money market funds are highly liquid and allow you to pull your money out at any time.